Re: [dpdk-dev] [PATCH] examples/ipsec-secgw: update incremental checksum

["Nicolau, Radu" <radu.nicolau@intel.com>]

> -----Original Message-----
> From: Akhil Goyal [mailto:akhil.goyal@nxp.com]
> Sent: Tuesday, January 16, 2018 6:30 AM
> To: Nicolau, Radu <radu.nicolau@intel.com>; dev@dpdk.org
> Cc: De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>;
> hemant.agrawal@nxp.com
> Subject: Re: [PATCH] examples/ipsec-secgw: update incremental checksum
> 
> Hi Radu,
> On 1/15/2018 8:10 PM, Nicolau, Radu wrote:
> >
> >
> >> -----Original Message-----
> >> From: Akhil Goyal [mailto:akhil.goyal@nxp.com]
> >> Sent: Monday, January 15, 2018 12:48 PM
> >> To: dev@dpdk.org
> >> Cc: De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>;
> >> hemant.agrawal@nxp.com; Nicolau, Radu <radu.nicolau@intel.com>
> >> Subject: Re: [PATCH] examples/ipsec-secgw: update incremental
> >> checksum
> >>
> >> On 1/15/2018 6:12 PM, Akhil Goyal wrote:
> >>> When TTL is decremented or ecn is updated in IP header before
> >>> forwarding the packet, checksum needs to be updated.
> >>>
> >>> In this patch an incremental checksum is added for ipv4 case.
> >>>
> >>> Signed-off-by: Akhil Goyal <akhil.goyal@nxp.com>
> >>> ---
> >> This patch is an update to a very old patch which was rejected earlier.
> >> http://dpdk.org/dev/patchwork/patch/16113/
> >>
> >>>    examples/ipsec-secgw/ipip.h | 19 ++++++++++++++++++-
> >>>    1 file changed, 18 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/examples/ipsec-secgw/ipip.h
> >>> b/examples/ipsec-secgw/ipip.h index fb6a6fa..13b8455 100644
> >>> --- a/examples/ipsec-secgw/ipip.h
> >>> +++ b/examples/ipsec-secgw/ipip.h
> >>> @@ -27,6 +27,10 @@ ipip_outbound(struct rte_mbuf *m, uint32_t
> >>> offset,
> >> uint32_t is_ipv6,
> >>>    	if (inip4->ip_v == IPVERSION) {
> >>>    		/* XXX This should be done by the forwarding engine instead
> >> */
> >>>    		inip4->ip_ttl -= 1;
> >>> +		if (inip4->ip_sum >= rte_cpu_to_be_16(0xffff - 0x100))
> >>> +			inip4->ip_sum += rte_cpu_to_be_16(0x100) + 1;
> >>> +		else
> >>> +			inip4->ip_sum += rte_cpu_to_be_16(0x100);
> >>>    		ds_ecn = inip4->ip_tos;
> >>>    	} else {
> >>>    		inip6 = (struct ip6_hdr *)inip4; @@ -95,8 +99,17 @@
> >>> ip6ip_outbound(struct rte_mbuf *m, uint32_t offset,
> >>>    static inline void
> >>>    ip4_ecn_setup(struct ip *ip4)
> >>>    {
> >>> -	if (ip4->ip_tos & IPTOS_ECN_MASK)
> >>> +	if (ip4->ip_tos & IPTOS_ECN_MASK) {
> >>> +		unsigned long sum;
> >>> +		uint8_t old;
> >>> +
> >>> +		old = ip4->ip_tos;
> >>>    		ip4->ip_tos |= IPTOS_ECN_CE;
> >>> +		sum = old + (~(*(uint8_t *)&ip4->ip_tos) & 0xff);
> >>> +		sum += rte_be_to_cpu_16(ip4->ip_sum);
> >>> +		sum = (sum & 0xffff) + (sum >> 16);
> >>> +		ip4->ip_sum = rte_cpu_to_be_16(sum + (sum >> 16));
> >>> +	}
> >>>    }
> >>>
> >>>    static inline void
> >>> @@ -140,6 +153,10 @@ ipip_inbound(struct rte_mbuf *m, uint32_t
> offset)
> >>>    			ip4_ecn_setup(inip4);
> >>>    		/* XXX This should be done by the forwarding engine instead
> >> */
> >>>    		inip4->ip_ttl -= 1;
> >>> +		if (inip4->ip_sum >= rte_cpu_to_be_16(0xffff - 0x100))
> >>> +			inip4->ip_sum += rte_cpu_to_be_16(0x100) + 1;
> >>> +		else
> >>> +			inip4->ip_sum += rte_cpu_to_be_16(0x100);
> >>>    		m->packet_type &= ~RTE_PTYPE_L4_MASK;
> >>>    		if (inip4->ip_p == IPPROTO_UDP)
> >>>    			m->packet_type |= RTE_PTYPE_L4_UDP;
> >>>
> >
> > I think instead of manipulating the checksum in this way it will be better to
> use rte_ipv4_cksum to re-compute it, unless the performance penalty is too
> significant.
> >
> There would be unnecessary wastage of cycles. This way of updating the
> checksum is implemented as per the RFC1141
> https://tools.ietf.org/html/rfc1141
> Do you see any issue in this way of updating the checksum?
No, I just tought that it will make the code look nicer.

Acked-by: Radu Nicolau <radu.nicolau@intel.com>